Blind rivets or fasteners are of the type in which only one side of the workpiece is accessible. In such fasteners, a stem and fastener body or sleeve are inserted as a unit into aligned openings in workpieces. The sleeve typically has a tail which engages the blind side of the workpieces and a head which engages the side of the workpieces which is accessible. A stem tail extending beyond the sleeve head is pulled from the accessible side of the sleeve causing a head on the stem, protruding beyond the sleeve tail to be drawn against the sleeve tail to deform it and create a head on the blind side of the workpieces. Once the sleeve has deformed, the workpieces are secured together, sandwiched between the head of the sleeve on the accessible side of the workpieces and the deformed head created on the blind side of the workpieces. Further pulling on the stem tail causes the stem to break at a predetermined location near the head of the sleeve, allowing removal of the excess stem portion protruding from the sleeve.
Many types of tools have been developed prior to this time for grasping a stem and pulling it through a sleeve to set a fastener. These tools have included pneumatic-hydraulic and hydraulically powered tools which use a piston to pull the stem of the fastener.
Many of these tools have suffered from the limitation that they required a secondary source of hydraulic or pneumatic pressure to power the piston. Such a requirement adds to the cost and complexity of such equipment. Further, when a secondary source of hydraulic or pneumatic pressure is required, the tool is not portable. The requirement that the secondary hydraulic or pneumatic source be attached to the tool during use prevents the tool from being used in many difficult to reach areas, as hoses and cords must be run from the secondary source to the tool. More commonly, the power source is not even available in repair situations.
Several hand powered tools have been developed for setting fasteners. These tools typically use a hydraulically operated piston to pull the rivet stem as well. Such tools, however, utilize the action of a hand pumped lever to create the hydraulic pressure necessary to move the piston. One such hand operated tool is disclosed in U.S. Pat. No. 4,263,801 to Gregory. This patent discloses a hand tool having a cylinder which has a piston located partially therein. The piston has a lateral bore with an intake port on one end and an exhaust port on the other, as well as a transfer chamber which is connected to a pressure chamber. A pump bore in the rear of the piston contains a plunger and opens into an inlet chamber. In order to operate the tool, a stem is inserted into one end of the piston, and the plunger is squeezed to force fluid from a reservoir into the inlet chamber and through the piston into the pressure chamber. The fluid pressure causes the piston to move away from a nose piece which is fixed to the cylinder and engages the sleeve. As the pressure in the pressure chamber increases, the piston is forced further away from the nose piece, at the same time pulling the stem through the sleeve, setting the fastener.
Several problems exist with the prior art hand powered fastener setting tools such as that described above. First, these tools have often been bulky and heavy, as dictated by the requirement that there be a mechanism by which sufficiently high hydraulic pressure may be generated so as to pull the stem. Second, the force necessary to actuate the pump or squeeze lever is often so high that it is not possible for a normal person to operate the tool in high pressure applications, or if it can be so operated, fatigue does not allow the tool to be maintained for use in setting many fasteners. This problem is caused by the fact that the ultimate upsetting force required to pull the stem, as well as the breaking strength of the stem, which the piston must apply to the stem, must be generated by pumping a handle to create high pressure fluid.
High pulling forces can be generated with only small squeezing or pumping forces, but there are adverse effects, that is, a tool with a small effective area about which the force is distributed requires only a small pumping force by an operator. At the same time, however, in such a device, each pump of the lever creates only a very small increment of fluid displacement, and thus piston movement. Thus, the lever must be squeezed many times to obtain the full piston stroke necessary to set the fastener. The high number of strokes which are necessary to set the fastener is inefficient from the standpoint that it takes a long time for the fastener to be set, and from the standpoint that it takes a great deal of operator energy to set each fastener.
Prior art fastener setting tools thus have not fulfilled the need for a hand operated tool which is light weight and compact, and which generates high pulling forces with low squeezing or pumping force, and at the same time is efficient to operate.